I think that's a combination of driving on a flat AND the tire itself being dryrotted. If the vehicle is parked and cycles through enough hot/cold days in the elements, it can really do a number of the rubber. Not all tires are create equal too. You should consider replacing your tires every 6 years according to the folks I've talked to. I actually got 11 out of the ones on my truck that only had 33k miles on them, but the rubber was cracking enough in places that I put up the $600 to replace them. Rubber gets old.
I actually had that happen to my pontoon trailer tire YESTERDAY. The tire was underinflated....which is more likely the cause for a blowout...but additionally, the tires were over 10 years old, so they likely are due for replacement anyhow considering the 2+ ton weight of the trailer + boat.
I was pretty lucky because I had just pulled the boat out and was still on the ramp when it blew out. I just backed up and launched the boat again to get the weight off the trailer. There was a guy there that saw me having trouble and gave me a wheel and tire he had in his truck that fit my trailer. I was then able to swap it out in the parking lot.
I then hopped in my boat and drove it back to my boathouse to fetch my 6 gallon pancake air compressor/tank. I drove 8 miles round trip on the lake to get the compressor/tank and topped off the tires....then got the boat out of there and on the trailer. It worked out. I'm going to be replacing those tires this Fall, from the looks of it...just to put new rubber on there.